US Edition Libyan officials said that the security forces had been withdrawn from al-Bayda city centre to avoid further loss of life, but were now laying siege to the town as an uprising turned into outright conflict.
Demonstrators in contact through social media with Libyan exiles claimed they also controlled parts of Libya's second city, Benghazi, and, in one unconfirmed report, had managed to prevent government planes bringing reinforcements landing at the airport.
Other social media from the country, which is largely closed to western journalists, showed bodies lying in hospitals as security forces fought back.
"The response of the people and the Revolutionary Forces to any adventure by these small groups will be sharp and violent," a statement from the Revolutionary Committees, the Gaddafi loyalists who notionally run the country, said on the website of a state newspaper, Green March.
The statement suggested the regime was preparing for a full-scale military response to the uprising, despite concessions including the closure of the national congress.
Human Rights Watch said it believed at least 16 had been killed in al-Bayda.
Anti-regime protests in eastern Libya cost the lives of at least 20 people in Benghazi and seven in Derna, the website of Oea newspaper, which is close to Col Gaddafi's son Seif al-Islam said.
"The security forces' vicious attacks on peaceful demonstrators lay bare the reality of Muammar Gaddafi's brutality when faced with any internal dissent," said Sarah Leah Whitson, who is Middle East and North Africa director for Human Rights Watch.
As in the early stages of the uprising in Egypt, prisons were attacked by relatives of inmates and there were reports both of mass escapes and of guards shooting inmates. Quryna said 1,000 inmates had broken out of a prison in Benghazi, while four prisoners were killed escaping from a jail in Tripoli.
Col Gaddafi, 68, is relatively young by the standards of some of his former neighbours such as ex-President Hosni Mubarak of Egypt, 82, but having come to power in 1969 he is the longest-serving leader in the Arab world.
He maintains his eccentric approach to governing his country, being filmed yesterday leading a midnight demonstration in support of himself to wildly cheering crowds in the capital Tripoli.
It is not clear how far strong opposition to his rule extends beyond Benghazi and al-Bayda in the east of the country, though activists were calling for a march in Jamahiriya Square in the capital on Twitter last night.
Elsewhere in the region, there were clashes and eight injuries when government supporters attacked protesters in Jordan, while at least two more people were killed as troops attacked protestors in Yemen. The deaths brought to five the victims of attempts by the authorities to break up repeated demonstrations against the rule of President Ali Abdullah Saleh this week.
A man set himself on fire in front of the presidential palace in Senegal on Friday and there were also reports of protests in the small Horn of Africa country of Djibouti.